It has been a constant problem in the art to provide satisfactory covers for truck body container beds having an open top, where those trucks are intended to carry materials which can spill from, or be blown from, the opened top of the bed during transit of the truck. Typically, in the art, the truck body opened-top container bed has been covered with tarpaulins, e.g. canvas tarpaulins, but such tarpaulins are difficult and time consuming to securely fasten to the open top of the bed, and in some cases, the fastening of a tarpaulin is a somewhat dangerous operation, in view of the height of the truck and the material being carried by the truck. Likewise, when the truck is to be unloaded, the tarpaulin must be removed, with the same disadvantages. Further, in view of the difficulties of attaching and removing the tarpaulin, many operators of such trucks are less than accurate in installing the tarpaulin, and during transit of a truck, it is a common experience for materials to be spilled or blown from trucks, even from trucks carrying a tarpaulin.
In view of the foregoing, the art has attempted to provide vertically displaceable, liftable tops for opened container bed trucks, but heretofore, these efforts have been, primarily, limited to small trucks, e.g. pick-up trucks, and the mechanisms for vertically displacing a liftable top have been somewhat complex, expensive to produce, and unsure in operation from a safety point of view. For example, U.S. Pat. No. 3,155,423 discloses a liftable truck top, but the mechanism used for that lifting requires extensive modification of the truck bed, is expensive to produce, and cannot provide assurance of the top being stably maintained in the lifted position. This latter concern is of particular importance in larger trucks, such as those described above, since the liftable top will be quite heavy, and should that liftable top collapse while the truck bed is being loaded, workers loading the truck could be seriously injured if struck by that top. Somewhat similarly, U.S. Pat. No. 3,765,716 discloses a liftable top and more positive locking for the top in the raised position, but here again, the mechanism for such lifting is complex, requires substantial modification of the truck, and is expensive to produce.
For relatively light liftable truck tops, especially for pick-up trucks and the like, the art has proposed more simple spring-loaded lifting arms, but here again, such mechanisms would not be appropriate for large trucks, such as described above, where the liftable top is relatively heavy, and U.S. Pat. No. 4,613,181 is representative thereof.
Another approach in the art is to provide a top which is tiltable relative to the truck bed, and here again, such mechanisms are useful only for relatively small trucks, such as pick-up trucks, and U.S. Pat. No. 4,819,981 is representative thereof.
On the other hand, for large trucks, such as the trucks noted above, and semi-trailer trucks, liftable covers have not been successful, primarily because the covers proposed in the art are complicated in the mechanisms for lifting, cannot provide positive assurance of the cover remaining in the lifted position while the truck is loaded or unloaded, and provide relatively little distance between the top of the bed of the truck and the underside of the cover when the cover is in the raised position, which severely limits the utility of the truck in terms of loading and unloading the truck, and U.S. Pat. No. 3,317,293 is representative thereof.
For large trucks of the present nature, in order to make a displaceable, liftable cover practical, the cover must be capable of being displaced with simple to operate mechanisms, such that extensive training, for safety purposes, is not necessary. The lifting mechanism must assure that the cover is lifted in a predictable manner, and when the cover is in the raised position, the cover must be vertically displaced from the bed of the truck a sufficient distance that easy access to the bed of the truck may be had by conventional loading equipment, such as a front-end loader. Also, when the cover is in the raised position, an automatic mechanism must be provided to ensure that the cover stays in that raised position during loading or unloading of the truck and that the cover cannot precipitously fall during such loading or unloading. It would, therefore, be a substantial advantage to the art to provide a displaceable, liftable truck cover with the foregoing characteristics.